(1) Field of the Invention
The present invention relates to a bus system in which a plurality of device units are connectible to the same bus, exemplified by a peripheral component interconnect (PCI) bus system employed in a storage system.
The invention also relates to a bus system design method suitable for designing the above bus system, and a device unit connectable to the bus system being in an active state.
(2) Description of Related Art
For example, a storage system which is equipped with a number of disk units (magnetic disk units, physical device units) and which is used for writing data from a server (host) to these disk units in response to access from the server or reading data requested by the server from the disk units and transmitting the data includes a host interface module, which controls interface (data transfer) with the server via a fiber channel interface bus.
The host interface module is connected to a PCI bridge module through an interface bus such as a PCI bus and transmits data to a disk interface module, management module, etc., connected to the PCI module through the PCI bus.
The host interface module is constructed as a single unit by mounting a central processing unit (CPU), a memory, and other devices on a printed-circuit board. If the thus-constructed host interface module is fitted or inserted in a mother board having a PCI bus, the device constituting the host interface module is communicably connected to the PCI bus. Installing a requisite number of interface modules to the mother board can easily fabricate a storage system equipped with the requisite number of host interface modules.
Mounting the host interface module on the PCI bus of the mother board being active (in a current-carrying state) (active insertion, active connection) generates a noise and has an adverse influence on the operation of other host interface modules connected on the PCI bus and operation of various devices constituting the mother board. This noise may be a cause of errors that occur in the above operations.
To prevent the adverse influence due to active insertion of host interface modules, operation of the PCI bus is generally stopped when a host interface module is fitted. For example, Japanese Laid-Open Patent Publication No. HEI 7-253834 (the below Patent Reference 1) discloses a module insertion/removal control device that inhibits noise propagating by connecting or disconnecting some of switches during active connection and disconnection, to prevent modules from failing or operating incorrectly.
However, if the bus operation of the PCI bus is stopped in order to insert a host interface module (i.e., the PCI bus is made non-active), data transmission through the PCI bus cannot be performed during the stoppage and therefore the data transmission efficiency is reduced. Also, since monitoring whether or not a host interface module has been inserted in the PCI bus and a variety of operations for stopping the PCI bus are needed, system control becomes complicated and system design efficiency is reduced.
Furthermore, addition of a dedicated control device for active insertion/removal (active connection) raise manufacturing costs and increases device size.
With the foregoing problems in view, the object of the present invention is to provide a bus system, a device unit, and a design method for the bus system, in each of which active connection of a device unit dose not affect other device units and devices that are connected to the same data bus.
Patent Reference 1: Japanese Laid-Open Patent Publication No. HEI 7-253834 (pages 3-4 FIGS. 1. 2.)